PCT Publication No. WO 93/13452, published Jul. 8, 1993 in the name of Capper, discloses a camera having an aiming mechanism. When a camera shutter button is partially depressed, the aiming mechanism produces a visible beam of light, for example a beam of laser light, which reflects off an object to be photographed, thereby indicating to the camera operator where the camera is aimed. The beam of laser light allows a camera operator to record images without having to look through a camera viewfinder to determine where the camera is aimed.
One of the chief advantages of a laser designator is that a high intensity spot is projected over a large distance with the divergence of the beam being determined by diffraction, which can be expressed mathematically using the laws of gaussian beam propagation. The high brightness of the laser spot makes it easy to recognize in what may be a busy scene being photographed.
When using laser light, it is important to assure that a person cannot be exposed to illumination power densities which exceed the human eye's damage threshold. These power densities are determined by laser safety standards which are set by various regulatory agencies. The illumination power density seen by the eye is determined by the power received at the pupil divided by the area of the pupil. The dilated pupil can reach about 7 mm in diameter. If the laser spot is incident on the pupil of a subject in a scene to be photographed, eye safety thresholds could be exceeded.
One way to solve this problem is simply to expand the beam to reduce its brightness However, such beam expansion reduces the observability of the laser designator to the photographer. As the distance from the camera to the scene increases, the expanded laser beam will begin to blend in with the scene illumination. As such, the laser designator will lose its effectiveness as an aiming mechanism.